Ammonium nitrate-cyanide explosive



nited States Patent Hammond, Ind., assignors to Standard Oil Company,

Chicago, 111., a corporation of Indiana No Drawing. Filed May 13, 1952, Ser. No. 287,623

1 5 Claims. (Cl. 149--6t)) This invention relates to new and improved explosive compositions. Particillarly, the invention relates to explosive compositions wherein ammonium nitrate is the principal gas-producing agent, More particularly, the invention relates to a readily ignitable' explosive comprising ammonium nitrate, Van ticular combustion catalyst. 1 Ammonium nitrateis widely used as a component of high explosives. Although ammonium'nitrate is classified as a high explosive, it is extremely insensitive and cannot readily bedetonated by the local application of heat or by a blasting cap; and when ignited, ammonium nitrate does not sustain propagation consistently. 'Normally'ammonium nitrate is mixed with an oxidizable material, such as, sulfur, carbon, cellulosic materials, hydrocarbons, etc., in order to utilize the excess oxygen available in the ammonium nitrate. However, these miX- tures of ammonium nitrate and oxidizable materials are also either very insensitive or slow burning.

One of the well known methods of overcoming this lack of sensitivity is to use a sensitive high explosive to prime the detonation of the ammonium nitrate explosive.

Exampleszof suitable primers are tetryl, TNT, nitrostarch, nitrocellulose, nitroglycerine, etc. An explosive that is detonable by the action of a blasting cap can be obtained by mixing the ammonium nitrate with the sensitive materials, such as, nitrostarch and nitrocellulose. The exoxid iz'able material and a par? 3,044,912 Patented July 17, 1962 2 temperature is expressed by R. N; Wimpress in Internal Ballistics of Solid-Fuel Rockets" (1950) as p h 1 "(1000) V wherein B is the linear burning rate,'p is the linear burning rate of the composition atfl OOO p.s.i.,'p is the pressure in p.s.i. and n is the exponent showing dependence of burning rate on pressure, i.e., pressure exponent. 7 Ammonium nitrate com-positions using chromium compound combustion catalyst have apressure, exponent of about 0.7. Smokeless powders such as ,ballistite' and cordite have a pressure exponent between about 0.6 and 0.7. A composition having a pressure exponent on the order of 1, readily passes into 'detonationwith only a small amount of tamping. A cheap, readily prepared and insensitive explosive having-a pressure exponent ofabout 1 'would be particularly useful for many commercial blastingoperations.

An object of this invention is the preparation of a new and improved ammonium nitrate explosive. Another object is the preparation of a readily ignitable explosive comprising ammonium nitrate and oxidizable material and a particular combustion catalyst, A particular object of the invention is an explosive mixture comprising ammonium nitrate and asphaltic hydrocarbon and a partreme sensitivity of these explosives makes them undesirable for ordinary blasting use.

Anothermethod'of obtaining a readily ignitable ammonium nitrate explosive is to admix therewith an organic sensitizer, such as, nitrogen compounds and certain carbohydrates. are obtained only when the sensitizer is very intimately dispersed throughout the mass. Generally this dispersion is obtainable only by the use of complicated and expensive procedures. 'I'he'mostcommonly used method for improving the sensitivity of ammonium nitrate explosives is to add a combustion catalyst. The commercially used combustion catalysts are all based on the element chromium. Themore common chromium combustioncatalysts are In general, satisfactory explosives 7 ammonium or alkali metalchromates or polychromates; I I

chromic oxide, chromic nitrate and copperchromite. The preferred material is ammonium 'dichromate. While the chromium compounds are the best known combus- .tion catalysts, they have the disadvantages ofbeingexticular burning catalyst, which mixturehas detonating properties.

The explosive mixture of this invention comprises a mixture of ammonium nitrate, an oxidizable material and an efiiecive amount of a combustion catalyst selected from the class of alkali metal-ferri cyanides and ammonium-ferri cyanides. In addition to the ammonium nitrate, moderate amounts of other inorganic nitrates, such as, potassium nitrate, sodium nitrate and magnesium nitrate may be present. The amount of combustion catalyst present will vary with the particular catalyst and somewhat with the particular oxidizable material present. In general between'about 0.5 and 25 weight percent of combustion catalyst may be present. The oxidizable material may be varied overa wide range. ever, the amount of oxidizable material should be maintained at a point such thatthe gas produced is soot-free. In general it is preferred that the explosive mixture be balanced with regard to oxidizable material and combustion catalyst in order to'produce a final mixture which is stoichiometrically balanced with respect to oxygen content. i V V I It has been discovered that certain'iron compounds are .elfective catalysts for sensitizing the ignition and the combustion of ammonium nitrate, particularly in the presence of an oxidizabl material other than the catalyst. When added. in sufficient quantity, these catalysts permit ammonium nitrate,;mixturesof ammonium nitrate and soor potassium nitrate; or mixtures of ammonium nitrate and oxidizable materials to'be ignited readily by theapplication of localized heat or bya commercial blasting cap. This combustion catalyst does not appreciably increase the shock sensitivity of'ammonium nitrate and causes only 'a moderate increase in the decomposition rateof ammonium nitrate at elevated temperatures. The

sired which has a detonating quality rather than the socalled deflagrating characteristic of the ordinary ammonium nitrate explosives. The burning characteristics of non-detonating explosives is dependent upon the temperature and pressure in the combustion chamber. The relationship of burning rate and pressure at constant particular combustion catalysts of this invention are selected fromthe group .consistirrgof alkali' metal-ferricyanides-and ammonium-ferricyanides. These" are so 'dium" ferricyanide, potassium ferricyanide and ammo nium ferricyanide. The combustion catalysts of this invention include those compounds which contain water. of hydration as well as the anhydrous form.

l A certain minimumamount of combustion catalyst is necessary in the explosive mixture or the mixture cannot be ignited. This minimum amount varies somewhat with the catalyst and with the type and amount of oxidizable Howweight percent of catalyst should be present. When operating with oxidizable materials in an amount such that the explosive mixture is approximately balanced, between about 0.5 and of catalyst should be present in the explosive mixture. 1

While the use of large amounts of the combustion catalyst of this invention will sensitize the ignition of ammonium nitrate alone or mixtures of ammonium nitrate and sodium nitrate alone, it is preferred to have an oxidizable material present in the explosive mixture. The decomposition of ammonium nitrate produces free oxygen; additional energy can be obtained by the presence of an oxidizable material which combines with this free oxygen. Any material which contains a deficiency of oxygen can be utilized. Metals such as aluminum and magnesium may be added. The non-metallic elements sulfur and carbon can be used. Nitrogen-containing organic compounds that do not unduly sensitize the explosive' mixture are particularly good; examples of these are urea, nitroguanidine, guanidine nitrate, and mononitrate naphthalene. Oellulosic materials are very desirable oxidizable materials, e.g., wood flour, cellulose acetate, etc. Hydrocarbon materials are a preferred oxidizable material. Examples of these are: paraflin waxes, petrolatum, high boiling hydrocarbon oils, tars, asphalts, bitumen, coal tar, shale oil residue, etc.

The mount of oxidizable material that may be added is dependent upon the particular type of material, but no more oxidizable material should be added than can react with the available oxygen to yield soot-free gas. When using hydrocarbon materials, in general, the maximum addition is between 20 and 25% by weight based on ammonium nitrate present. It is preferred to use explosive mixtures which are stoichiometrically balanced with respect to oxygen content.

The viscous hydrocarbons are a preferred oxidizable material because the explosive mixtures containing these hydrocarbons have a pressure exponent on the order of 1. Examples of these viscous hydrocarbon materials are waxes, petrolatums, viscous lubricating distillates, reduced crudes, industrial fuel oils, cracked tars, asphalts, either natural or blown, bitumen, coal tar, shale oil resids. In general the amount of hydrocarbon material which may be present may vary from between Sand 25 weight percent, based on explosive mixture. It is preferred to use an amount-of hydrocarbon which will produce an explosive mixture that is stoichiometrically balanced with respect to oxygen.

The explosive mixture of this invention is illustrated by several examples. Test grains of the desired composition were made as follows: When necessary, the ammonium nitrate was ground in a mortar to break up small lumps. The desired amount of ammonium nitrate, oxidizable material and combustion catalyst were weighed into a beaker and the contents thereof were thoroughly mixed. The mixture was extruded by means of a laboratory-size extruder to form a grain about inch in diameter and 6 inches long. In order to insure uniformity, duplicate grains were made and tested in each example. The burning characteristics of each explosive mixture were deter? mined after inhibiting the cylindrical surface of the grain with a thin layer of either asphalt or a cellulose base thermoplastic suchas cellulose acetate. The inhibited grain was placed in a bomb and the bomb brought to the desired operating pressure by the use of cylinder nitrogen. At this time the grain was ignited and the burning rate in inches per second was determined; each burning rate is an average of at least two trials.

There are set out below four examples of compositions which are approximately in balance with respect to oxygen. In three of the examples an asphalt prepared from a cracked tar and having a softening point of about 100 C. was the oxidizable materialand intheother a mixture of oxygenated hydrocarbons was used as a binder. In Examples 1 and 4 sodium ferrocyanide was the combustion catalyst, and in Example 2 potassium ferricyanide was the combustion catalyst.

K3Fe(CN)a, wt. percent. 4 Burning rate, 1,000 p.s.i 0.09 0.10 0.10 Burning rate, 1,600 p.s.i 0.13 0.18 0.13 Pressure Exponent 0. 1. 15 0. 68

1 Would not burn.

9 Cellulose acetate, 4.9% dinitrodiphenyl oxide, 9.9%

ethylene glycol diglycolate, 9.9%. Particularly outstanding is the pressure exponent in Example 2, wherein potassium ferricyanide was used as the burning catalyst. The difference in pressure exponent between Examples 1 and 4 indicates that oxygenated hydrocarbons do not give mixtures having detonating properties when using sodium ferrocyanide as the combustion catalyst.

The term ammonium nitrate as used in this specification and in the claims is intended to mean either ordinary commercial grade ammonium nitrate, such as, conventionally grained ammonium nitrate containing a small amount of impurities and which is then generally coated with a small amount of moisture-resisting material such as petrolatum or parafiin, or military grade ammonium nitrate, or a mixture of other inorganic nitrates and ammonium nitrate wherein the ammonium nitrate is the preponderate nitrate.

The explosive mixture can be made by milling the ingredients or by dry mixing; this operation is preferably followed by forming regular shaped compacted grains by pressing the powdered mix in molds. It is preferred to prepare the shaped grains by adding the powdered ammonium nitrate to fused organic or oxidizable material at l00-125 C., mixing to form a paste, and pressing the paste into suitable molds. The cooledgrains are strong and durable.

Having described the invention, what is claimed is:

1. An explosive composition consistingessentially of a binder, a combustion catalyst and ammonium nitrate, wherein the binder is a viscous hydrocarbon and is present in an amount between about 5 and 25 weight percent, the combustion catalyst is selected from the class consisting of alkali-metal ferricyanides and ammonium-ferricyanides and is present in an amount between about 0.5 and 25 weight percent and the remainder is essentially all ammonium nitrate.

' 2. The composition of claim 1 wherein said catalyst is present in an amount between about 0.5 and 10 weight percent.

3. The composition of claim 1 wherein said catalyst is potassium-ferricyanide. I

4. The composition of claim 1 wherein said binder is asphalt.

5. A detonating explosive mixture which consists essentially of ammonium nitrate, about 81%; asphalt, about 45% and potassium-ferricyanide, about 4%.

References Cited in the file of this patent UNITED STATES PATENTS 

1. AN EXPLOSIVE COMPOSITION CONSISTING ESSENTIALLY OF A BINDER, A COMBUSTION CATALYST AND AMMONIUM NITRATE, WHEREIN THE BINDER IS A VISCOUS HYDROCARBON AND IS PRESENT IN AN AMOUNT BETWEEN ABOUT 5 AND 25 WEIGHT PERCENT, THE COMBUSTION CATALYST IS SELECTED FROM THE CLASS CONSISTING OF ALKALI-METAL FERRICYANIDES AND AMMONIUM-FERRICYANIDES AND IS PRESENT IN AN AMOUNT BETWEEN ABOUT 0.5 AND 25 WEIGHT PERCENT AND THE REMAINDER IS ESSENTIALLY ALL AMMONIUM NITRATE. 